Carbonaceous Particles in the Atmosphere: Experimental and Modelling Issues

Carbonaceous particles and their organic component are one of the major combustion by-products and they are recognized to play a relevant role in radiative transfer, air quality, and human health, due to their fine-submicrometric nature. These effects are magnified by transboundary air masses transport of natural fires plumes or anthropogenic emissions from domestic heating and industrial activities, affecting not only the source areas. In fact, analysis on snow samples from different arctic sites revealed the presence of carbonaceous particulate matter, with biomass burning identified as responsible for more than 90% of these particles. As a consequence of this deposition, snow albedo variations are added to the other factors influencing Earth’s radiative budget. For these reasons, there is a growing interest toward the above-mentioned arguments, but there is also a need to assess the role of carbonaceous particles and to review the different measurements techniques, highlighting their limitations and uncertainties. The papers included in this special issue improve the comprehension of processes involving carbonaceous particles considering them under different points of view because both experimental and modeling approaches are examined

Morphologies and elemental compositions of local biomass burning particles at urban and glacier sites in southeastern Tibetan Plateau: Results from an expedition in 2010

Many studies indicate that the atmospheric environment over the southern part of the Tibetan Plateau is influenced by aged biomass burning particles that are transported over long distances from South Asia. However, our knowledge of the particles emitted locally (within the plateau region) is poor. We collected aerosol particles at four urban sites and one remote glacier site during a scientific expedition to the southeastern Tibetan Plateau in spring 2010. Weather and backward trajectory analyses indicated that the particles we collected were more likely dominated by particles emitted within the plateau. The particles were examined using an electron microscope and identified according to their sizes, shapes and elemental compositions. At three urban sites where the anthropogenic particles were produced mainly by the burning of firewood, soot aggregates were in the majority and made up >40% of the particles by number. At Lhasa, the largest city on the Tibetan Plateau, tar balls and mineral particles were also frequently observed because of the use of coal and natural gas, in addition to biofuel. In contrast, at the glacier site, large numbers of chain-like soot aggregates (similar to 25% by number) were noted. The morphologies of these aggregates were similar to those of freshly emitted ones at the urban sites: moreover, physically or chemically processed ageing was rarely confirmed. These limited observations suggest that the biomass burning particles age slowly in the cold, dry plateau air. Anthropogenic particles emitted locally within the elevated plateau region may thus affect the environment within glaciated areas in Tibet differently than anthropogenic particles transported from South Asia. (C) 2018 Elsevier B.V. All rights reserved

Characterization of isoprene-derived secondary organic aerosols at a rural site in North China Plain with implications for anthropogenic pollution effects

Isoprene is the most abundant non-methane volatile organic compound (VOC) and the largest contributor to secondary organic aerosol (SOA) burden on a global scale. In order to examine the influence of high concentrations of anthropogenic pollutants on isoprene-derived SOA (SOA(i)) formation, summertime PM2.5 filter samples were collected with a three-hour sampling interval at a rural site in the North China Plain (NCP), and determined for SOA(i) tracers and other chemical species. RO2+NO pathway derived 2-methylglyceric acid presented a relatively higher contribution to the SOA, due to the high-NOx (similar to 20 ppb) conditions in the NCP that suppressed the reactive uptake of RO2+HO2 reaction derived isoprene epoxydiols. Compared to particle acidity and water content, sulfate plays a dominant role in the heterogeneous formation process of SOA(i). Diurnal variation and correlation of 2-methyltetrols with ozone suggested an important effect of isoprene ozonolysis on SOA(i) formation. SOA(i) increased linearly with levoglucosan during June 10-18, which can be attributed to an increasing emission of isoprene caused by the field burning of wheat straw and a favorable aqueous SOA formation during the aging process of the biomass burning plume. Our results suggested that isoprene oxidation is highly influenced by intensive anthropogenic activities in the NCP

Sources and formation of carbonaceous aerosols in Xi'an, China:Primary emissions and secondary formation constrained by radiocarbon

To investigate the sources and formation mechanisms of carbonaceous aerosols, a major contributor to severe particulate air pollution, radiocarbon (C-14) measurements were conducted on aerosols sampled from November 2015 to November 2016 in Xi'an, China. Based on the C-14 content in elemental carbon (EC), organic carbon (OC) and water-insoluble OC (WIOC), contributions of major sources to carbonaceous aerosols are estimated over a whole seasonal cycle: primary and secondary fossil sources, primary biomass burning, and other non-fossil carbon formed mainly from secondary processes. Primary fossil sources of EC were further sub-divided into coal and liquid fossil fuel combustion by complementing C-14 data with stable carbon isotopic signatures. The dominant EC source was liquid fossil fuel combustion (i.e., vehicle emissions), accounting for 64 % (median; 45 %-74 %, interquartile range) of EC in autumn, 60 % (41 %-72 %) in summer, 53 % (33 %-69 %) in spring and 46 % (29 %-59 %) in winter. An increased contribution from biomass burning to EC was observed in winter (similar to 28 %) compared to other seasons (warm period; similar to 15 %). In winter, coal combustion (similar to 25 %) and biomass burning equally contributed to EC, whereas in the warm period, coal combustion accounted for a larger fraction of EC than biomass burning. The relative contribution of fossil sources to OC was consistently lower than that to EC, with an annual average of 47 +/- 4 %. Non-fossil OC of secondary origin was an important contributor to total OC (35 +/- 4 %) and accounted for more than half of non-fossil OC (67 +/- 6 %) throughout the year. Secondary fossil OC (SOCfossil) concentrations were higher than primary fossil OC (POCfossil) concentrations in winter but lower than POCfossil in the warm period. Fossil WIOC and water-soluble OC (WSOC) have been widely used as proxies for POCfossil and SOCfossil, respectively. This assumption was evaluated by (1) comparing their mass concentrations with POCfossil and SOCfossil and (2) comparing ratios of fossil WIOC to fossil EC to typical primary OC-to-EC ratios from fossil sources including both coal combustion and vehicle emissions. The results suggest that fossil WIOC and fossil WSOC are probably a better approximation for primary and secondary fossil OC, respectively, than POCfossil and SOCfossil estimated using the EC tracer method

Fine Particulate Matter Constituents and Cardiopulmonary Mortality in a Heavily Polluted Chinese City

Background: Although ambient fine particulate matter (PM2.5; particulate matter ≤ 2.5 µm in aerodynamic diameter) has been linked to adverse human health effects, the chemical constituents that cause harm are unknown. To our knowledge, the health effects of PM2.5 constituents have not been reported for a developing country

Gaseous, PM2.5 Mass, and Speciated Emission Factors from Laboratory Chamber Peat Combustion

Peat fuels representing four biomes of boreal (western Russia and Siberia), temperate (northern Alaska, USA), subtropical (northern and southern Florida, USA), and tropical (Borneo, Malaysia) regions were burned in a laboratory chamber to determine gas and particle emission factors (EFs). Tests with 25 % fuel moisture were conducted with predominant smoldering combustion conditions (average modified combustion efficiency (MCE) =0.82+/-0.08). Average fuel-based EFCO2 (carbon dioxide) are highest (1400 +/- 38 g kg(-1)) and lowest (1073 +/- 63 g kg(-1)) for the Alaskan and Russian peats, respectively. EFCO (carbon monoxide) and EFCH4 (methane) are similar to 12 %15 % and similar to 0.3 %0.9 % of EFCO2, in the range of 157171 and 310 g kg(-1), respectively. EFs for nitrogen species are at the same magnitude as EFCH4, with an average of 5.6 +/- 4.8 and 4.7 +/- 3.1 g kg(-1) for EFNH3 (ammonia) and EFHCN (hydrogen cyanide); 1.9+/-1.1 g kg(-1) for EFNOx (nitrogen oxides); and 2.4+/-1.4 and 2.0 +/- 0.7 g kg(-1) for EFNOy (total reactive nitrogen) and EFN2O (nitrous oxide). An oxidation flow reactor (OFR) was used to simulate atmospheric aging times of similar to 2 and similar to 7 d to compare fresh (upstream) and aged (downstream) emissions. Filter-based EFPM2.5 varied by \u3e 4-fold (1461 g kg(-1)) without appreciable changes between fresh and aged emissions. The majority of EFPM2.5 consists of EFOC (organic carbon), with EFOC / EFPM2.5 ratios in the range of 52 %98 % for fresh emissions and similar to 14 %23 % degradation after aging. Reductions of EFOC (similar to 79 g kg(-1)) after aging are most apparent for boreal peats, with the largest degradation in low-temperature OC1 that evolves at \u3c 140 degrees C, indicating the loss of high-vapor-pressure semivolatile organic compounds upon aging. The highest EFLevoglucosan is found for Russian peat (similar to 16 g kg(-1)), with similar to 35 %50 % degradation after aging. EFs for water-soluble OC (EFWSOC) account for similar to 20 %62 % of fresh EFOC. The majority (\u3e 95 %) of the total emitted carbon is in the gas phase, with 54 %75 % CO2, followed by 8 %30 % CO. Nitrogen in the measured species explains 24 %52 % of the consumed fuel nitrogen, with an average of 35 +/- 11 %, consistent with past studies that report similar to 1/3 to 2/3 of the fuel nitrogen measured in biomass smoke. The majority (\u3e 99 %) of the total emitted nitrogen is in the gas phase, with an average of 16.7 % as NH3 and 9.5 % as HCN center dot N2O and NOy constituted 5.7 % and 2.9 % of consumed fuel nitrogen. EFs from this study can be used to refine current emission inventories

Step pyrolysis of N-rich industrial biowastes: Regulatory mechanism of NOx precursor formation via exploring decisive reaction pathways

Step pyrolysis of N-rich industrial biowastes was used to explore decisive reaction pathways and regulatory mechanisms of NOx precursor formation. Three typical ones involving medium-density fiberboard waste (MFW), penicillin mycelia waste (PMW) and sewage sludge (SS) were employed to compare the formation characteristics of NOx precursors during one-step and two-step pyrolysis. Results demonstrated that considerable NH3-N pre-dominated NOx precursors for one-step pyrolysis at low temperatures, depending on primary pyrolysis of labile amide-N/inorganic-N in fuels. Meanwhile, NOx precursors differed in the increment of each species yield while resembled in the total yield of 20-45 wt.% among three samples at high temperatures, due to specific prevailing reaction pathways linking with distinctive amide-N types. Subsequently, compared with one-step pyrolysis uniformly (800 degrees C), by manipulating intensities of reaction pathways at different stages (selecting differential intermediate feedstocks), two-step pyrolysis was capable of minimizing NOx precursor-N yield by 36-43% with a greater impact on HCN-N (75-85%) than NH3-N (9-37%), demonstrating its great capacity on regulating the formation of NOx precursors for industrial biowaste pyrolysis. These observations were beneficial to develop effective insights into N-pollution emission control during their thermal reutilization

The linkages with fires, vegetation composition and human activity in response to climate changes in the Chinese Loess Plateau during the Holocene

Holocene paleo-records of the Chinese Loess Plateau loess-soil profiles were used to reconstruct wildfire patterns and landscape evolution. We examine black carbon and charcoal influx, combined with the Magnetic susceptibility, delta C-13 values of soil organic matter, pollen counts and other paleo-environmental proxies to discuss interactions with biomass-climate during the Holocene. The history of fires from the charcoal and black carbon (BC, char and soot) influx at the two sites demonstrates a transition from climate-controlled low amplitude variations with peaks during the Early and Middle Holocene (11-3.1kyearsB.P.) to higher amplitude variability in fire occurrence decoupled from climate and tied to human activities during the Late Holocene (3.1-0kyearsB.P.). The difference in fire patterns was attributed to regional effective moisture and human land use over the entre Loess Plateau; meanwhile, fire activities observed during the Holocene are consistent with variations in vegetation composition inferred from delta C-13 values in soil organic matter, pollen counts, and paleoclimate proxies. Regional wildfires rarely occurred on the desert steppe dominated by a weedy C-3 taxon (Artemisia, Compositae, and Chenopodiaceae dominated)during the late glacial period. A limited biomass would not meet fire propagation in the extreme colder and drier environment of the Loess Plateau during those periods, though. As the climate became ameliorated during the early Holocene, there was an increasing biomass and a sufficient contribution do to high fuel accumulation from C-4 taxon (Gramineae). As the middle Holocene progressed toward warmer and wetter conditions, fire events were less frequent on the steppe and forest-steppe (e.g. expansion of trees C-3,C- Quercus, Corylus) of the Loess Plateau. Subsequently, the number of local and regional fire events have largely increased with the colder and drier climate conditions (e.g. expansion of C-3 weedy), which have been decoupling with intensive anthropogenic burning for farming since the past 3kyr. These data suggests that the regional fire patterns vary strongly along environmental gradients in the effective moisture and regional fuel availability as well as the spatial and temporal distributions of Neolithic burning practices over the Loess Plateau in response to the weakening East Asian monsoon during the Holocene